Interaction of leukocytes with platelet microparticles derived from outdated platelet concentrates

Platelet microparticles (PMP) were isolated from outdated platelets by a co mbination of differential centrifugation and gel filtration, and the concen tration of PMP was expressed in the equivalent of GPIIb/IIIa complex measur ed by captured ELISA. PMP bound to isolated neutrophils and macrophages in a dose-dependent manner, but they did not bind to lymphocytes, Incubation o f PMP with neutrophils did not activate these cells as measured by up-regul ation of Mac-1, release of human granulocyte elastase, and calcium mobiliza tion. Incubation of PMP with macrophages did not enhance IL-8 production an d the oxygen burst but slightly and significantly increased production of M CP-I. After 10 min incubation of PMP with macrophages, an increase of GPIIb /IIIa antigen was observed suggesting that PMP may be endocytosed by macrop hages. In conclusion, PIMP bind to leukocytes, but, in contrast to activate d platelets, do not play a significant role in leukocyte activation.